BAB 6 Buku Standardisasi Spesifikasi Teknis Transformator Tenaga 30MVA (SK DIR NO.0632.K-DIR-2013)

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BUKU STANDARDISASI

SPESIFIKASI TEK NIS

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BUKU STANDARDISASI

SPESIFIKASI TEKNIS

TRANSFORMAT

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Keputusan Direksi PT PLN (Persero) Nomor : 0632.K/DIR/2013 Tanggal : 17 Oktober 2013

SAMBUTAN

DIREK TUR UTAMA

Assalamualaikum Warahmatullahi Wabarakatuh

Buku Standardisasi Spesifikasi Teknis Transformator Tenaga dan Penjelasannya ini

merupakan himpunan spesifikasi teknis Transformator yang disusun dengan pertimbangan beragamnya spesifikasi Transformator tenaga di unit pembangunan dan pengelola penyaluran yang menyulitkan saat enjinering, pengadaan, konstruksi, operasi, pemeliharaan dan penyediaan material cadang.

Dengan memperhatikan permasalahan di atas maka dirasa perlu untuk melakukan standardisasi spesifikasi transformator tenaga yang memperhatikan kualitas peralatan, kebutuhan sistem, keselamatan ketenagalistrikan, efisiensi, kemudahan konstruksi dan pemeliharaan penyaluran. Dengan terbitnya Buku Standardisasi Spesifikasi Teknis Transformator Tenaga ini maka spesifikasi teknis transformator tenaga yang dibuat oleh unit pengelola penyaluran dalam rangka pengadaan transformator tenaga harus mengacu pada standar ini.

Pada kesempatan ini pula, disampaikan terima kasih yang sebesar-besarnya kepada seluruh anggota TIM Penyusun Buku Spesifikasi Transformator Tenaga PT PLN (Persero) yang telah bekerja keras dan meluangkan waktu, tenaga dan pikiran untuk menyelesaikan Buku Standardisasi Spesifikasi Transformator Tenaga ini. Semoga Allah SWT memberikan pahala dan berkah-Nya kepada seluruh anggota Tim.

Wassalamualaikum Warahmatullahi Wabarakatuh

Direktur Utama

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TIM PENYUSUN

BUKU STANDARDISASI SPESIFIKASI TEKNIS

TRANSFORMATOR TENAGA

1. Eko Yudo Pramono NIP. 7094998 JA

2. Djoko Mulyadi NIP. 5886006 K3

3. Jati Pharmadita NIP. 8610306 Z

4. Ratnasari Sjamsuddin NIP. 6994025 P

5. Nugraha Rohman NIP. 6593070Z

6. Sumaryadi NIP. 6684317 K3

7. Campy Hidayat NIP. 6383022 LMK

8. Ahmad Muhaymin NIP. 6294030 LMK

9. Ahmad Fauzan NIP. 8510331 Z

10. Tanjung Anggraini NIP.8208459 Z

11. M. Husen Hatala NIP. 8109026Z

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DAFTAR ISI

SAMBUTANDIREKTUR UTAMA ... 1

TIM PE NYUSUN ... 2

DAFTAR ISI ... 3

TECHNICAL PARTICULAR AND GUARANTEE ... 5

1. TRANSFORMATOR DAYA 66/20 KV 30 MVA ... 5

2. TRANSFORMATOR DAYA 150/20 KV 30 MVA ... 17

3. TRANSFORMATOR DAYA 150/20/10 KV 60 MVA ... 29

4. INTER BUS TRANSFORMER 150/70/10 KV 60 MVA ... 41

5. INTER BUS TRANSFORMER 150/70/10 KV 100 MVA ... 53

6. INTER BUS TRANSFORMER 275/150/20 KV 83.3 MVA (KONVENSIONAL) ... 65

7. INTER BUS TRANSFORMER 275/150/20 KV 83.3 MVA (AUTOTRANSFORMER) .... 79

8. INTER BUS TRANSFORMER 275/150/66 KV 167 MVA (AUTOTRANSFORMER) ... 93

9. INTER BUS TRANSFORMER 500/150/71.5 KV 167 MVA (SINGLE PHASE) ... 106

10. INTER BUS TRANSFORMER 500/150/71.5 KV 500 MVA (THREE PHASE) ... 118

TECHNICAL SP ECIFICATIONS ... 130 1. GENERAL ... 130 1.1. WORK INCLUDED ... 130 1.2. QUALITY STANDARDS ... 130 1.2.1. GENERAL ... 130 1.2.2. STANDARDS ... 130 1.2.3. CONFLICTS ... 131 1.3. SITE CONDITION ... 131 1.4. SERVICE CONDITION ... 131 1.5. SUBMITTALS... 131 1.5.1. LANGUAGE ... 131 1.5.2. DOCUMENTS TO BE SUBMITTED ... 131

1.6. TESTING AND INSPECTION ... 132

2. SPECIFIC REQUIREMENTS ... 132

2.1. TYPES AND MAIN PERFORMANCES ... 132

2.1.1. FAULT CONDITIONS ... 133

2.1.2. LOSSES ... 134

2.1.3. VIBRATION AND NOISE ... 134

2.1.4. HARMONIC SUPPRESSION ... 134

2.1.5. IMPEDANCE AND REGULATION ... 135

2.1.6. TRANSFORMER GENERAL LAYOUT ... 135

2.2. MAGNETIC CIRCUIT AND WINDINGS ... 137

2.2.1. MAGNETIC CIRCUIT ... 137

2.2.2. MAGNETIC POLARIZATION (FLUX DENSITY) ... 137

2.2.3. WINDINGS ... 137

2.2.4. INTERNAL EARTHING ARRANGEMENTS ... 138

2.3. TANKS ... 139

2.3.1. MAIN TANK ... 139

2.3.2. CONSERVATOR TANK ... 141

2.3.3. PRESSURE RELIEF DEVICE ... 141

2.3.4. OIL HANDLING FACILITIES ... 141

2.3.5. JOINT FACES ... 142

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2.4. COOLING SYSTEM ... 143

2.4.1. GENERAL ... 143

2.4.2. RADIATORS/FORCED AIR COOLERS CONNECTED DIRECTLY TO TANK ... 143

2.4.3. AIR BLOWERS ... 143

2.4.4. COOLER CONTROL ... 144

2.5. VOLTAGE CONTROL ... 144

2.5.1. GENERAL ... 144

2.5.2. ELECTRICAL REMOTE CONTROL ... 145

2.5.3. INDICATION AND ALARMS ... 146

2.5.4. AUTOMATIC VOLTAGE CONTROL ... 146

2.5.5. VOLTAGE REGULATION RELAY ... 147

2.5.6. REMOTE CONTROL PANEL ... 147

2.5.7. MARSHALLING BOX ... 148

2.5.8. CONTROL PRINCIPLE ... 149

2.6. PROTECTIVE DEVICES ... 149

2.6.1. TEMPERATURE INDICATING DEVICE ... 149

2.6.2. BUCHOLZ RELAY ... 150

2.7. DRYING OUT... 150

2.8. BUSHING INSULATORS ... 150

2.9. CABLE TERMINATIONS ... 152

2.10. CABLES AND TERMINATIONS ... 153

2.10.1.CABLE BOXES AND SEALING END CHAMBERS ... 153

2.10.2.DISCONNECTING CHAMBERS ... 153

2.10.3.TESTING ... 153

2.10.4.SUPPLY OF CABLES ... 153

2.11. SPARE PARTS FOR S/S TRANSFORMERS ... 154

2.12. INSULATING OIL ... 154

2.12.1.FILLING WITH OIL ... 154

2.12.2.SUPPLY OF TRANSFORMER OIL... 154

2.13. PRE-APPROVED SUPPLIER LIST ... 154

2.14. PREPARATION FOR TRANSPORT ... 156

2.15. TESTS ... 156

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KE PUTUSAN DIREKS I PT P LN (PER SERO) Nomor : 0632.K/DIR/2013 Tanggal : 17 Oktober 2013

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2. Transformator Daya 150/20 kV 30 MVA

TECHNICAL PARTICULAR AND GUARANTEE

Transformator Daya 150/20/10 kV 30 MVA

NO. DESCRIPTION UNIT SPECIFIED

1 GENERAL

1.1 Standards IEC 60076 series, SPLN T3.002, SPLN 61

1997

1.2 Factory to be stated by bidder

1.3 Type and design number to be stated by bidder

1.4 Installation on site Outdoor

1.5 Service conditions :

a. Maximum altitude meter 1000

b. Temperature of ambient air and cooling medium

°C 40

c. Average monthly air temperature °C 30 d. Average annual ambient

temperature

°C 30

1.6 Installation environment

a. Dust pollution rate heavy or very heavy

b. Seismic disturbance g 0,25

2 RATING AND PERFORMANCE

2.1 Number of phase per unit 3

2.2 Number of winding per phase 3

2.3 Purpose of tertiary winding stabilizing

2.4 Vector group YNyn0+d

2.5 Rated power (Sr) :

a. For primary & secondary winding

- Stage 1 (100% Sr) MVA 30

- Stage 2 (80% Sr) MVA N.A.

- Stage 3 (60% Sr) MVA 18

b. Tertiary winding

- Stage 1 (100% Sr) MVA 10

- Stage 2 (80% Sr) MVA N.A.

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TECHNICAL PARTICULAR AND GUARANTEE

2.6 Highest voltage (Um) for equipment :

a. Primary winding kV 170

b. Secondary winding kV 24

c. Tertiary winding kV 12

2.7 Rated voltage (Ur) :

2.8 Highest voltage (Um) for neutral point:

a. Primary winding kV 17,5

2.9 Tapping of primary winding (minimum) :

a. Number of steps 16

b. Number of taps 17 (-8 to +8)

c. Numbering of tap positions 1 to 17

d. Tapping factor (Ud/Ur) % 1,25

2.10 Short-circuit impedance (at 75 °C, rated power)

a. At principal tap % 12,5

b. At maximum tap % to be stated by bidder

c. At minimum tap % to be stated by bidder

2.11 Voltage drop (or rise) as % of rated voltage at full load,

At power factor 1 & 75 °C :

a. At principal tap % to be stated by bidder

At power factor 0.8 & 75 °C :

2.12 Percent reactance drop at full load, power factor 1 & 75 °C

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TECHNICAL PARTICULAR AND GUARANTEE

2.13 Percent resistance drop at full load, power factor 1 & 75 °C

2.14 Rated current :

a. Primary winding A 115,5

b. Secondary winding A 787,3 (at 22kV)

c. Tertiary winding A 333,3 (phase current) 2.15 Lightning impulse withstand voltage:

2.16 Switching impulse withstand voltage:

a. Primary winding kV N.A.

b. Secondary winding kV N.A.

c. Tertiary winding kV N.A.

2.17 Power frequency withstand voltage:

2.18 Symmetrical short-circuit withstand current (2 seconds) :

a. Primary terminals kA 40

b. Secondary terminals kA 25

c. Tertiary terminals kA N.A.

2.19 Minimum efficiency (at 75 °C, 50 Hz, continuous rated power, at principal tap) :

a. power factor 1 % 99,75

b. power factor 0.8 % 99,65

2.20 Highest efficiency and its load point

- Stage 1 (100% Sr) % (> point 2.19.a) at . . . . % - Stage 2 (80% Sr) % (> point 2.19.a) at . . . . % - Stage 3 (60% Sr) % (> point 2.19.a) at . . . . %

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TECHNICAL PARTICULAR AND GUARANTEE

2.21 Maximum no-load current at principal tap :

a. For rated voltage % In 0,2

b. For 105 % of rated voltage % In to be stated by bidder c. For 110 % of rated voltage % In to be stated by bidder

at rated voltage & principal tap 2.23 Maximum load loss at continuous

rated power

b. At minimum tap kW to be stated by bidder c. At maximum tap kW to be stated by bidder

d. Power for cooling fans kW 2

e. Power for cooling pumps kW N.A.

2.24 Hot spot factor 1,3

2.25 Maximum temperature rise (refer to point 1.5 d)

a. Average winding K 55

b. Top oil K 50

c. Hot spot K 68

2.26 Maximum winding hot spot temperature (refer to point 1.5 d)

a. Long Emergency overload °C 120

b. Continous loading °C 98

2.27 Sound pressure level at 100% rated voltage: - Stage 1 (100% Sr), measuring distance 2 m dB 71 - Stage 2 (80% Sr), measuring distance 2 m dB N.A. - Stage 3 (60% Sr), measuring distance 0,3 m dB 67 3 CORE

3.1 Core Materials (IEC 60404)

a. Steel Sheet material Grain Oriented Hi-B silicon steel, Laser or Non Laser steel

b. Name of factory of sheet steel AK Steel / POSCO Steel / Nippon Steel / ThyssenKrupp Steel/ JFE

c. Thickness mm 0.23 / 0.27

2.22 Maximum no-load loss at 50 Hz, kW 18

(75 °C, 50Hz, power factor 1) :

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TECHNICAL PARTICULAR AND GUARANTEE

3.2 Minimum Magnetic polarization for H = 800 A/m

Tesla 1,85

3.3 Maximum specific core loss at 1.7 Tesla, 50 Hz

Watt/kg max 0.95

3.4 Maximum flux density

a. Continuous rated power Tesla 1,7

b. Worst emergency condition Tesla 1,88 3.5 Minimum weight of core ton to be stated by bidder

4 WINDINGS

4.1 Conductor

a. Conductor material high purity copper

b. Conductor manufacturer

- Primary winding ASTA / Metrod / Essex / Shenyang - Secondary winding ASTA / Metrod / Essex / Shenyang - Tertiary winding ASTA / Metrod / Essex / Shenyang c. Minimum total conductor weight

including insulation

to be stated by bidder d. Winding configuration

- Primary winding disc / helical

- Secondary winding disc / helical

- Tertiary winding multi layer / layer / disc / helical e. Winding insulation

- Primary winding to be stated by bidder

- Secondary winding to be stated by bidder

- Tertiary winding to be stated by bidder

4.2 Insulation paper

a. Insulation material thermally upgraded paper b. Insulation paper manufacturer Weidmann / Munksjö / Pucaro

c. Class of insulation (Class A)

d. Minimum degree of polimerization after Oven process

900

4.3 Uniform/graded design of winding insulation :

`

a. Primary winding graded

b. Secondary winding uniform

c. Tertiary winding uniform

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TECHNICAL PARTICULAR AND GUARANTEE

4,5 Maximum current density :

a. Primary winding A/mm² 2,5

b. Secondary winding A/mm² 2,5

c. Tertiary winding A/mm² 3,25

4,6 Phase connections :

a. Primary winding star

b. Secondary winding star

c. Tertiary winding delta

4,7 Connection of OLTC primary windings at the neutral side 5 ON LOAD TAP CHANGER

5.1 Design in-tank mounted

5.2 Type MR Vacutap (Germany)

5.3 Construction :

a. selector switch yes

b. diverter switch & tap selector yes

c. change over selector yes

5.4 Driving mechanism :

a. manual operation below cover yes

b. motor drive yes

c. with o/c circuit breaking yes

5.5 Motor drive unit type MR ED 100

5.6 Completed with transducer for tap position indicator

yes

6 OIL

6.1 Main tank and on load tap changer oil type

- Uninhibited Certified Nepthanic Base

6.2 Oil manufacturer Nynas Libra / Shell S2 - ZU I / Total Isovoltine II

6.3 Corrosive sulphur Non-corrosive (IEC 60296)

6.4 Oil preservation system - Rubber Bag + Maintenance free dehydrating breather

a. Rubber bag manufacturer Pronal / Fujikara / Musthane b. Dehydrated breather manufacturer MR - MTraB / Comem

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TECHNICAL PARTICULAR AND GUARANTEE

6.5 Volume of Oil (min) kl to be stated by bidder 7 TERMINATIONS

7.1 Termination for phases :

a. Primary oil to air or oil to SF6 or oil to oil bushing

b. Secondary oil to air bushing

c. Tertiary oil to air bushing

7.2 a. Termination for primary and secondary neutrals

bushings b. Terminations for one corner of

delta tertiary winding

bushings

7.3 Primary and Secondary bushings Primary Secondary a. Name of Manufacturer & Type HSP / ABB - Micafil /

ABB / Alstom

NGK / HSP / Knobel / Comem / Cedaspe

/ Alstom

b. Insulator Porcelain Porcelain

c. Type of insulation Resin Impregnated Paper

non-condenser d. Internal conductor : to be stated by

bidder to be stated by bidder - Type to be stated by bidder to be stated by bidder - Cross section mm² to be stated by

bidder

to be stated by bidder - Outer terminal Cylindrical stud Cylindrical stud

- Material of outer terminal Copper Copper

- Connection details Draw Rod to be stated by

bidder

- Bottom contact Yes Yes

- Material of bottom contact Copper Copper

e. Highest voltage (Um, r.m.s. values)

kV 170 24

f. Rated current A min. 1250 2500

g. Rated short-time current (2 seconds)

kA 40 ≥ 16

h. Dry impulse withstand voltage kV 750 145

i. Switching impulse withstand voltage

kV N.A. N.A.

j. Power-frequency test voltage

1 min wet (r.m.s. values) kV 325 50

k. Maximum dielectric dissipation factor (tan delta) at power frequency

% 0.5 N.A.

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TECHNICAL PARTICULAR AND GUARANTEE

7.4 Dimension Primary Secondary

a. CT Space / facility (L4) 300 to be stated by

bidder b. Flange to bottom end nut (L1) 720 to be stated by

bidder

c. Flange Diameter (D3) 335 to be stated by

bidder d. Hole to Hole diameter (D2) 290 to be stated by

bidder

7.5 Bushing current transformer Primary Secondary

a. Core 1 N.A. N.A.

b. Core 2 N.A. N.A.

c. Core 3 N.A. N.A.

d. Core 4 N.A. N.A.

7.6 Tertiary bushings Tertiary 1 Tertiary 2

a. Name of Manufacturer & Type NGK / HSP / Knobel / Comem / Cedaspe

b. Insulator Porcelain Porcelain

c. Type of insulation non-condenser non-condenser d. Internal conductor : to be stated by

bidder to be stated by bidder - Type to be stated by bidder to be stated by bidder - Cross section mm² to be stated by

bidder

to be stated by bidder - Outer terminal Cylindrical stud Cylindrical stud

- Material of outer terminal Copper Copper

- Connection details to be stated by bidder

to be stated by bidder

- Bottom contact Yes Yes

- Material of bottom contact Copper Copper

e. Highest voltage (Um, r.m.s. values)

kV 12 12

f. Rated current A min. 1600 1600

g. Rated short-time current (2 seconds)

kA ≥ 16 ≥ 16

h. Dry impulse withstand voltage kV 75 75

i. Switching impulse withstand voltage

kV N.A. N.A.

j. Power-frequency test voltage

1 min wet (r.m.s. values) kV 28 28

k. Dielectric dissipation factor (tan delta)

% N.A. N.A.

7.7 Neutral bushings : Primary Secondary

- Manufacturer and type NGK / HSP / Knobel / Comem / Cedaspe

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TECHNICAL PARTICULAR AND GUARANTEE

8 COOLING SYSTEM : 8.1 Cooling method

a. Stage 1 (100% Sr) ONAF

b. Stage 2 (80% Sr) N.A.

c. Stage 3 (60% Sr) ONAN

8.2 Radiator mounted on tank yes

8.3 Radiator height Higher than main tank with swan neck type

8.4 Number of group of radiator to be stated by bidder 8.5 Number of radiator per group pcs to be stated by bidder 8.6 Radiator and tube bundle rust

protection

hot dip galvanized and painting

8.7 Number of group of cooling fan to be stated by bidder 8.8 Number of cooling fan per group pcs to be stated by bidder 8.9 Cooling fan motor :

a. Nominal voltage (1ph. / 3 ph.) V 230 / 400 b. Nominal power of each motor kVA to be stated by bidder 8.10 Life of cooling fan (operating hour) hour to be stated by bidder

8.11 Number of cooling pump N.A.

8.12 Cooling pump motor : N.A.

a. Nominal voltage (1ph. / 3 ph.) V N.A. b. Nominal power of each motor kVA N.A.

c. Operation hour counter N.A.

9 MAIN TANK AND CONSERVATOR 9.1 Main tank materials :

a. Name of factory to be stated by bidder

b. Design cover type

c. Grade of steel to be stated by bidder

d. Thickness (top /wall/base) mm to be stated by bidder 9.2 The minimum withstand-pressure of

main tank :

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TECHNICAL PARTICULAR AND GUARANTEE

9.3 Conservator tank design : (main & oltc oil separated)

a. Name of factory to be stated by bidder

b. cylindrical/box-type cylindrical

c. Grade of steel to be stated by bidder

d. Thickness (top/wall/base) mm to be stated by bidder e. Oil level indicator type visual window and magnetic type 9.4 Conservator tank mounting :

a. attached above main tank yes

b. For delivery : separated yes

9.5 Air-sealed conservator with dehydrated breather (Rubber Bag)

yes

9.6 Type & number of construction of oil drain assembly

to be stated by bidder (for oil sampling, online DGA,

filtering, vaccuum)

9.7 Type and number of construction of slide valves

9.8 Type of sealings and gaskets :

a. asbestos fibre to be stated by bidder

b. oil-proof rubber yes

9.9 Tank rust protection :

a. rust-proofing yes

b. marine coated painting yes

c. name & type of paint to be stated by bidder

d. colour RAL 7032

9.10 Bottom base design skid

10 CONTROL AND INDICATION

10.1 Marshalling box degree of protection IP 55

10.2 Control and Indication local & remote ; manual & electrical 10.3 DC Supply for control and indication Vdc 110

10.4 Supply voltage for motor of on load tap changer, fan,

Vac 230 / 400

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TECHNICAL PARTICULAR AND GUARANTEE

10.5 Temperature monitor

a. Oil temperature OTI

b. Winding temperature WTI

c. Hot spot temperature fiber optic for type test unit only 10.6 Fiber optic temperature sensor

a. Sensor manufacturer Neoptix / Luxtron

b. Sensor type / designation to be stated by bidder c. Completed with temperature

monitor

yes

b. Number of sensors 3 at each HV, LV, and TV windings (9 total) 11 PROTECTION

11.1 Buchholz relay :

a. manufacturer & Type EMB / COMEM / Qualitrol b. waterprof contacts and

microswitches

yes c. Maintenance Valves at both sides Required

d. Protection functions gas accumulation, insulation liquid loss insulation liquid flow surge

e. Gas collector for buchholz relay yes

11.2 Overpressure relay for on load tap changer :

a. manufacturer & Type MESSKO / Qualitrol b. waterprof contacts and

microswitches

yes

c. maintenance valves at both sides yes

11.3 Provision for fire prevention system yes 11.4 Pressure Relief Device

a. Type MESSKO / Qualitrol

b. Completed with cover yes

11.5 Ingress protection rating of relays and terminals box

IP66

12 WEIGHT AND DIMENSION

12.1 Weight of tank and fitting ton to be stated by bidder 12.2 Weight of active part ton to be stated by bidder

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TECHNICAL PARTICULAR AND GUARANTEE

12.4 Height of the top point m to be stated by bidder

12.5 Total length m to be stated by bidder

12.6 Total width m to be stated by bidder

12.7 Maximum height of lifting during assembly or maintenance

m to be stated by bidder

12.8 Largest package :

- Weight ton to be stated by bidder

- Dimensions (H x L x W) m x m x m

12.9 Heaviest package :

- Weight ton to be stated by bidder

- Dimensions (H x L x W) m x m x m

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TECHNICAL SPECIFICATIONS

POWER TRANSFORMER

1. GENERAL 1.1. WORK INCLUDED

The Work includes design, manufacturing, tests and inspection, packing and shipping, foundation guide design, guarantee as specified of substation power transformers including accessories, and the followings if specified: custom clearance, inland transportation, site assembly and site test.

1.2. QUALITY STANDARDS

1.2.1. GENERAL

Equipment/materials testing, cleaning, services and reports to meet the general and specific requirements including technical particulars and drawings (if any) of this specification, specified standards, codes and other applicable standards.

1.2.2. STANDARDS

In summary the equipment/materials shall conform to the latest applicable standards of sponsor organizations not limited to the followings:

SNI : Standard Nasional Indonesia

SPLN : Standar Perusahaan Listrik Negara

SPLN 8 (Series) : TransformatorTenaga

SPLN 61 : SpesifikasiTransformatorTenagaTeganganTinggi

SPLN T3.002 : TeganganPengenalTransformatorTenaga Dan

JangkauanPenyadapanPengubahSadapanBerbebanPada System 66 kV, 150 kV, 275 kV, dan 500 kV

Unless specified otherwise or modified herein, all IEC standards (e.g. with the following series numbers) are directly or indirectly applicable, including parts and addenda:

60060 : High voltage test techniques

60076 (Series) : Power transformers

60137 : Insulating bushings for alternating voltages above 1000V

60214 (Series) : On-load tap-changers

60270 : Partial discharge measurements

60296 (Series) : Specification for insulating oils 60404 (Series) : Magnetic materials

60567 : Oil-filled electrical equipment – Sampling of gasses and of oil

for analysis of free and dissolved gases – Guidance.

60599 : Mineral oilimpregnated electrical equipment in service

-Guide to the interpretation of dissolved and free gases analysis

60616 : Terminal and tapping markings for power transformers

60529 : Degrees of protection by enclosures (IP Code)

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1.2.3. CONFLICTS

a. If conflicting requirements among applicable standards exist, the most stringent one shall govern.

b. If this specification conflicts in any way with applicable standard(s), this_{specification shall take precedence and shall govern.}

1.3. SITE CONDITION

The equipment shall be suitable for operation under site service condition as specified in Technical Particulars and Guarantees (TPG).

1.4. SERVICE CONDITION

The equipment will be installed outdoor and will be subject to the minimum and maximum environmental conditions asspecified in Technical Particulars and Guarantees (TPG).

The equipment shall be suitable for operation under the ambient conditions specific to their respective location while in service.

1.5. SUBMITTALS

1.5.1. LANGUAGE

All documents are to be written inBahasa Indonesia and/or English

1.5.2. DOCUMENTS TO BE SUBMITTED

The following data shall be submitted: When Bidding

a. Preliminary outline drawings showing dimensions and arrangement/ position of major external features including conservator, terminals, cooling equipment and other essential appurtenances. These drawings shall show parts and masses to be removed for transportation.

b. Technical particulars and guarantee

c. Type test certificate for each type of transformers and accessories for the same rating (Voltage and Capacity) or higher

d. Technical literature on the equipment

e. Satisfactory Operation Statement Letter from users f. Certificate of ISO-9001 (Latest Version)

g. Quality Manual for Review & Acceptance h. Other data if requested during evaluation. After the Award of the Contract

a. Foundation guide drawings

b. Outline and detail drawings referring to appropriate engineering practices_{or as requested for approval} c. Calculation note:

- Losses

- Temperature Rise

- Short Circuit

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f. Method of Inspection and Testing

- Type Test and Routine Test Procedure

- Factory Acceptance Test Procedure

- Site Acceptance Test Procedure

g. Test report (Type Test and Routine Test) in hard copy and soft copy before delivery

h. Transportation procedure and acceptance criteria i. As built drawings in hard copy and soft copy

j. Operating and maintenance instructions in hard copy and soft copy.

1.6. TESTING AND INSPECTION

The equipment is subject to inspection and test by the Purchaser/Engineers during the course and on completion of manufacture to ensure compliance with this specification and to provide the necessary data.

The Bidder may submit type test certificate of test which has been carried out on

identical equipment. Not withstand any provision in standard the

Purchaser/Engineers shall have the right to reject such certificate in lieu of the specified test.

During the manufacturing process, Purchaser has the right to audit the transformer manufacturer and component suppliers according to Quality Assurance / Quality Control procedure of PLN, on Purchaser’s expense if necessary. Audit result can be used by the Purchaser to accept or reject the transformers.

Factory Acceptance Test (FAT)shall be carried out by the Manufacturer and will be witnessed by the Purchaser or Purchaser Engineers. The Manufacturer shall prepare all completed transformers (including accessories) of each batch ready for routine test to be witnessed by Purchaser or Purchaser Engineers. All costs or expenses in all cases of Factory Acceptance Test shall be borne by the Bidder. The Bidder shall guarantee that the Manufacturer will provide all things necessary for the carrying out the required tests including electric power, instruments, temporary connections, etc.

All instruments used in tests shall carry calibration certificates from an accredited testing laboratory and shall perform within the limits of error necessary to carry out the tests satisfactorily. The instruments are subject to the approval of the Purchaser Engineer.

The Bidder shall supply to the Purchaser, as soon as practicable after tests, necessary copies of the relevant test certificates which shall contain details of each test performed, records, results and calculations shall also be provided. If any item fails to comply with the requirements for a test, the Purchaser may reject the item or defective component thereof whichever he considers necessary and after replacement, adjustment or modification as directed by the Purchaser, the Bidder shall repeat the tests as necessary to demonstrate compliance with the specification at his extra cost.

2. SPE CIFIC REQUIREMENTS

2.1. TYP ES AND MAIN PERFORMANCES

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winding currents at nominal and highest/rated voltages of 3 phase 50 Hz power system.

The transformers shall comply with the quality standards specified (clause 1.2) and their current carrying capacity shall be limited only by the capacity of the core and coils, not by other current carrying components such as on-load tap changer or bushings.

The voltages between phases on the higher and lower voltage windings measured at no load shall be those corresponding to the normal ratios of transformation. On load tap changer shall be provided at the primary side for varying the ratio of transformation using tapping as stipulated on the technical particular and guarantee.

The transformer shall have capacity and other ratings as specified at the ambient

temperature 30°C and shall comply with IEC 60076-2 as regards the corrected

temperature rise (maximum 55°C for windings and 50°C for oil) and IEC 60076-7

for over loads on all tapping irrespective of power flow direction and with secondary voltage winding at the specified nominal voltage.

Each transformer shall be fitted with tank mounted coolers capable of dissipating the losses at continuous maximum rating (CMR) without the measured winding hot

spot temperature exceeding 98°C.

In more detail, the requirements are listed in the Technical Particulars and drawings (if any).

2.1.1. FAULT CONDITIONS

It is to be assumed that the amount of generating plant simultaneously connected is such that normal voltage will be maintained on one side of any transformer when there is a short circuit between phases or any phase to earth on the other side.

The winding shall be capable of withstanding the forces to which it is subjected under all conditions, particularly the forces due to a short circuit between terminals or between any terminal and earth, with full voltage maintained on all other windings intended for connection to external sources of supply and allowing for any feed back through windings connected to rotating machines.

Evidence shall be submitted with the proposal to prove with calculations according to IEC 60076-5 the ability of each type of transformer to withstand, on any tapping, fault conditions as described below:

• Thermal ability to withstand short-circuit

Average temperature of each windings shall not exceed 200⁰C with the

duration of symmetrical short-circuit current to be used for calculation of the thermal ability to withstand short circuit shall be 4 seconds.

• Dynamic effects of short circuit

Theoretical evaluation of the ability to withstand dynamic effects of short circuit shall result force or stress figures which are 30 % less than values stipulated in Annex A of IEC 60076-5:2006.

The proposal shall include a brief description of those transformers or parts thereof which have been subjected to short circuit tests or for which short circuit calculations are available.

It is preferred that this information relates to designs comparable with the transformers offered but in the event this is not so the Purchaser reserves the right to require calculations to prove that the design of transformers offered will

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IEC 60076-5.

2.1.2. LOSSES

The Bidder shall complete the Technical Particulars form, values for components of losses comprisingnoload loss, load loss at continuous maximum rating (C.M.R.) and auxiliary loss if any.

The total losses shall be as low as is consistent with transport restrictions, reliability and economic use of materials.

The Bidder shall state the maximum losses including tolerance. If the losses measured on test exceed the guaranteed values, then the Contract Price for the transformer shall be reduced in proportion to the amount by which the losses measured on tests exceed the guaranteed losses.

The cost of losses:

No-load loss at Rupiah per kW

Rp86.063.698,-Load lossat Rupiah per kW

Rp55.080.766,-Cooling fanat Rupiah per kW

Any transformer shall be rejected after Factory Acceptance Test (FAT) if the losses exceed the guaranteed value by an amount in the following:

Total Losses 10%

Component Losses 15% (unless the total loss exceed 10%) 2.1.3. VIBRATION AND NOISE

The transformers shall be so designed and constructed that harmful vibration is eliminated and that no avoidance noise will occur at any operating conditions. The level of vibration shall not adversely affect any clamping or produce excessive stress in any material and the noise must be as low as possible.

Measurement of noise level of any transformer and auxiliaries shall be in accordance with the IEC 60076-10whichever the lowest and the measured values shall not exceed the figures specified in the Technical Particulars. Noise level tests to be carried out on all transformers.

2.1.4. HARMONIC SUPPRESSION

Transformers shall be designed with particular attention to the suppression of harmonic voltages, especially the third, fifth,and seventhharmonics and to minimize the detrimental effects or interference with communication circuit resulting therefore.

Tertiary Winding (for 150/20 kV and 150/66 kV transformers):

The tertiary or stabilizing winding is required for the purpose of suppressing harmonics.

To avoid the effect of over-voltage, one corner of this winding is to be brought out through 2 bushings (for test and measurement) on the tank and will be directly grounded.

Due to the shifting of one corner to earth point, the insulation of tertiary windings to all part including to tapping winding shall be designed adequately.

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2.1.5. IMPEDANCE AND REGULATION

The Bidder shall state in the Schedule of Technical Particulars and Guarantee the values of impedance measured on principal and extreme tapping and the voltage regulation from no load to C.M.R. at unity power factor and at 0.8 lagging power factor with constant voltage across the higher voltage windings.

2.1.6. TRANSFORMER GENERAL LAYOUT

Transformers shall be designed with general layout as following: 1. HV Bushing 2. HVN Bushing 3. LV Bushing 4. LVN Bushing 5. TV Bushing 6. Marshalling Kiosk 7. Conservator 8. Tap Changer

9. Tap Changer Motor Drive Unit 10. Radiator

11. Fire Protection 12. Base Plate

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1 phase transformer

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2.2. MAGNETIC CIRCUIT AND WINDINGS

2.2.1. MAGNETIC CIRCUIT

The design of the magnetic circuit shall be such as to avoid static discharges, development of short circuit paths internally or to the earthen clamping structure, and the production of flux components normal to the plane of the laminations. Each lamination shall be insulated with a material stable under the action of pressure and hot oil.

The winding structure and major insulation shall be designed to permit an unobstructed flow of cooling oil through core cooling oil ducts to ensure efficient core cooling.

The magnetic circuit shall be insulated from all structural parts, and shall be capable of withstanding a test voltage to core bolts and to the frame of 2500 volts rms for one minute.

2.2.2. MAGNETIC POLARIZATION (FLUX DENSITY)

Core shall be constructed of non-aging, high permeability cold rolled grain oriented silicon steel sheets of the Hi-B or higher grade having minimum magnetic polarization value of 1.85 Tesla at 800 A/m and maximum specific total loss 0.95 -1 Watt/kg at -1.7 Tesla and 50 Hz. Adequate evidence for the supply from the steel sheets manufacturer shall be provided before/during inspection/tests.

The steel sheets shall be properly annealed after cutting to suitable sizes and rolled to insure smooth surfaces at the edges. Both sides of each sheet shall be carlite-coated and insulated with heat resisting varnish to minimize eddy current losses.

The cores shall be carefully assembled and rigidly, strongly enough clamped to insure adequate mechanical strength to support the windings and to prevent shifting/displacement of laminations during shipment, transportation, operation, short circuit or other stresses and also to reduce vibration/noise to a minimum under operating conditions.

The clamping frames must be insulated against the sheets.

2.2.3. WINDINGS

The transformer windings shall be constructed from high conductivity copper and assembled in a manner as best suited for the particular application. The application of ZnO is not allowed in any part of the windings.

Proper consideration shall be given to all factors of service such as high dielectric and mechanical strength of insulation, coil characteristics and minimum restrictions to the free circulation of oil.

Coil shall be made up, shaped and braced to provide for expansion and contraction due to temperature changes in order to avoid abrasion of insulation and to provide rigidity to resist movement and distortion caused by abnormal operating conditions, and shock during shipment and transportation.

Adequate barriers shall be provided between windings and core and between high voltage and low voltage windings. End coils shall have additional protection against abnormal line disturbances.

The entire design, construction and treatment of the windings and their assembly on the core shall embody the latest improvements.

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which are made mechanically stable and solid.

The assembled core and coils shall be dried under a vacuum condition, immediately impregnated, and immersed in dry oil.

The 150 kV star connected windings shall have thermally upgraded paperaccording to IEC-60076-7. Thermally upgraded paper is cellulose-based paper which has been chemically modified to reduce the rate at which the paper decomposes. Ageing effects are reduced either by partial elimination of water forming agents (as in cyanoethylation) or by inhibiting the formation of water through the use of stabilizing agents (as in amine addition, dicyandiamide). A paper is considered as thermally upgraded if it meets the life criteria defined in ANSI/IEEE C57.100; 50 % retention in tensile strength after 65 000 hours in a

sealed tube at 110 °C or any other time/temperature combination given by the equation (see IEC 60076-7).

All transformer windings below 150 kV shall have uniform insulation as defined in IEC-60076-7.

The neutral terminal shall be permanently connected to earth, directly or through a current transformer, but without any intentionally added impedance in the connection. The separate source AC withstand voltage shall be at least 38 kV for one minute.

The insulation shall be provided against attack by mouldsand other tropical effect and shall be tropicalized according with the related standards.

The transformers shall be designed to withstand the impulse voltage levels and the power frequency voltage tests specified in the Schedule of Technical Particulars.

The windings shall be located in a manner which will ensure that they remain electrostatically balanced and that their magnetic centers remain coincident under all conditions of operation.

The windings shall also be thoroughly seasoned during manufacture by the application of axial pressure at a high temperature for such length of time as will ensure that further shrinkage is unlikely to occur in service.

All electrical connections within windings shall be brazed to withstand the shocks which may occur through rough handling and vibration during transport, switching and other transient service conditions.

Coil clamping rings shall be of non magnetic steel or insulating material built up from flat laminations. Axially laminated material other than bakelised paper is not to be used.

Where bakelised paper rings are used with the layers of paper lying in the axial direction, the rings may be relied upon to provide the major insulation between the windings and frame, subject to there being adequate creepage distance.

Any metal pieces in contact with laminated rings shall be designed and secured so that they do not weaken the electrical or the mechanical properties of the rings. If the winding is built up of sections or of disc coils separated by spacers, the clamping arrangements shall ensure that equal pressures are applied to all columns of spacers.

2.2.4. INTERNAL EARTHING ARRANGEMENTS

All metal parts of the transformer, with the exception of the individual core lamination, core bolts, and associated individual clamping plates, shall be

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The top main core clamping structure shall be connected to the tank body by a copper strap and the bottom main core clamping structure shall be earthen by one or more of the following methods:

(a) by connection through vertical tie rods to the top structure.

(b) by direct metal-to-metal contact with the tank base maintained by the weight

of the core and windings.

(c) by connection to the top structure on the same side of the core as the main

earth connection to the tank.

The magnetic circuit shall be earthen to the clamping structure at one point through a removable link placed in an accessible position just beneath an inspection opening in the tank cover and which, by disconnection, will enable the insulation between the core and clamping plates, etc. to be tested at voltages up to 2.5 kV for the purpose of checking deterioration during service. The connection to the link shall be on the same side of the core as the main earth connection. These requirements are compulsory.

Magnetic circuits having an insulated sectional construction shall be provided with a separate link for each individual section and the arrangement of the connections shall be subject to the approval of the Purchaser/Engineer.

Where oil ducts or insulated barriers parallel to the plane of the laminations divide the magnetic circuits into two or more electrically separate parts, the ducts and insulating barriers which have the thickness greater than 0.25 mm are to be bridged with tinned copper strips so inserted as to maintain electrical continuity. Where coil clamping rings are of metal at earth potential, each ring shall be connected to the adjacent core clamping structure on the same side of the transformer as the main earth connection.

Main earthing connections shall have a cross-sectional area of not less than 80 sqmm but connections inserted between laminations may have cross-sectional areas reduced to 20 sqmm when in close thermal contact with the core.

2.3. TANKS

2.3.1. MAIN TANK

Each transformer shall be enclosed in a suitably stiffened welded steel tank such that the transformer can be lifted and transported without permanent deformation or oil leakage. The construction shall employ weldable structural steel.

Lifting lugs shall be provided suitable for the weight of the transformer including core and windings, fittings, and with the tank filled with oil. Each tank shall be provided with at least four jacking lugs, and with lugs suitably positioned for trans-port on a beam transtrans-porter. They must be rated for the most unfavourable load distribution on two diagonals.

The base of the tank shall be so designed that it is possible to move the complete transformer unit in any direction without injury when using rollers, plates or rails. Transformers shall have skid bases. Detachable under-bases must not be used. If wheelbases are requested, the device for fastening the rollers on the rails is part of delivery. The rails shall also be supplied of the quality at least St 37 and finished with hot dip galvanization.

All joints, other than those which may have to be broken shall be welded. Defective welded joints may be re-welded subject to the written approval of the Purchaser/Engineer.

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construction which will be oil-tight and gas-tight.

For bell type design of the tank, the bottom joint between the tank and base shall be provided with suitable flanges and gaskets having sufficient and properly spaced bolts so that the assembly will be oil-tight and gas-tight.

All gaskets shall be made of high quality material, which will not deteriorate under tropical and site service conditions specified.

The tank shall have sufficient strength, not distort when lifted and to withstand an internal pressure and also external pressure under a vacuum without damage or permanent deformation.

The transformer tank shall be capable of withstanding without deflection exceeding the values stated in clause 2.15. vacuum of 508 mm of mercury less than atmospheric pressure when empty of oil, or the vacuum required by the recommended drying-out procedure, whichever is the greater.

The tank and cover shall be designed in such a manner as to leave no external pockets in which water can lodge, no internal pocketsin which oil can remain when draining the tank or in which air can be trapped when filling the tank, and to provide easy access to all external surfaces for painting. The interior surface of the tanks shall be painted with an oil resistant coat, the exterior surface with a primer and two finish coats.

Each radiator bank shall be connected to the main tank through flanged valves mounted on the tank at top and bottom, and each bank shall be fitted with drain valve and air release plug.

Inspection openings shall be provided to give access to the internal connections of bushings, winding connections and earthing links. Each opening shall be currently located and must be of ample size for the purpose for which it is intended. All inspection covers shall be provided with lifting handles.

It must be possible to remove any bushing without removing the tank cover. Pockets shall be provided for a stem type thermometer and for the bulbs of temperature indicators. These pockets shall be located in the position of maximum oil temperature and it must be possible to remove any bulb without lowering the oil level in the tank. Captive screwed caps shall be provided to prevent the ingress of water to the thermometer pockets when they are not in use.

Whether accommodation shall be provided for bushing current transformers or for outdoor weatherproof neutral current transformers for primary/secondary side of each type are specified in the Technical Particulars.

The transformer shall be provided with globe-type or butterfly-type valves as required for:

- Drain valve

- Oil sampling incl. facilities - Lower filter press connection. - Upper filter press connection - Isolating each radiator (in-let) - Isolating each radiator (out-let) -Isolating the both sides of bucholz - Isolating the both sides of OLTC relays

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oil without leaking.

The transformer shall be provided with pressure release device(s), a ladder for inspection with anti-climbing plate, cable conduits for wiring of relay and current transformer circuits, and rod type thermometer shall be mounted in a well so that it can be changed without lowering oil in the tank.

To facilitate installation, center marks, level marks and center of gravity marks shall be provided at suitable portions of the tanks or bases.

The Contract shall include the design of transformer foundation pads.

2.3.2. CONSERVATOR TANK

Each transformer shall be provided with an overhead conservator tankformed of substantial steel plates and arranged above the highest point of the oil circulating system. Connections to the main tank shall be at the highest point to prevent the trapping of air or gas under the main tank cover.

The capacity of each conservator tank shall be adequate for the expansion and contraction of oil in the whole system under the specified operating conditions. Conservator tanks shall also be provided with a cleaning door, filling cap, drain valve with captive cap, and magnetic oil level gauges for main tank oil & OLTC oil. The conservator tank shall be so located that it does not obstruct the passage of high voltage conductors immediately above the transformer.

Each conservator shall be fitted with an oil seal type breather with rubber bag and silica-gel containers sized as listed below. The breather shall be mounted at a height of approximately 1.4 meters above ground level. The breather shall be maintenance free dehydrating breather type.

2.3.3. PRESSURE REL IEF DEVICE

An approved pressure relief device of sufficient size for rapid release of any pressure that may be generated in the main and OLTC tank, and designed to operate at a static pressure lower than the hydraulic test pressure specified shall be provided.

The relief device is to be mounted on the tank cover and means are to be provided to deflect gas accumulation into the Buchholz relay and not to collect in the relief device.

The device shall not permit the ingress of moisture. Visible means/alarm shall be provided for indicating that the relief device has operated. Provision shall also be added to trip the HV side CB for serious conditions following oil surge.

Pressure relief devices must be full covered with lateral openings for transformer tank and OLTC. The trip contacts (IP65) must be directly activated by a self-locking signal pin. Release time must be within 2ms. All important parts like trip contacts, springs, must be mounted inside.

2.3.4. OIL HANDLING FACILITIES

Each transformer shall be fitted with the following valves as a minimum requirement:

Main tank:

(a) One 50 mm bore filter valve located near to the top of the tank.

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the tank to ensure that the tank can be completely drained of oil as far as is practicable.

(d) One valve for oil sampling incl. sampling facilities.

(e) Two valves for isolating both sides (in-let & out-let) of each radiator.

(f) One valve for isolating bucholz relay.

Main Conservator Tank:

(e) One drain valve for oil conservator tank so arranged that the tank can be

completely drained of all oil and sampling facilities.

(f) One valve to cut off oil supply to the bucholz relay.

OLTC Conservator Tank:

(g) One valve for oil drain and sampling facilities.

(h) One valve to cut off oil supply to the OLTC tank

OLTC Tank:

(i) Oil drain and sampling facilities.

(j) One valve in oil surge relay pipe-work where appropriate.

Valves shall be of the sluice type, have non-rising spindles and shall be closed by turning the hand-wheel in a clockwise direction. They shall have machined flanges and provision for locking in the closed and open positions. Details of the locking devices shall be clearly shown on the general arrangement drawing.

Every valve shall be provided with an indicator to show clearly the positionof the valve, and each hand-wheel shall be fitted with a non-corrosive nameplate with engraved and filled letters or figures to provide an approved inscription which will indicate the purpose of the valve.

Blank flanges, plates or captive screw caps shall be fitted to all valves and pipe ends not normally connected in service.

The omission of any of, or the provision of alternative arrangements to, the aboverequirements will not be accepted unless approved in writing by the Purchaser/Engineer before manufacture.

2.3.5. J OINT FACES

All joint faces shall be arranged to prevent the ingress of water or leakage of oil with a minimum of gasket surface exposed to the action of oil or air.

Oil resisting synthetic rubber gaskets are not permissible except where the synthetic rubber is used as a bonding medium for cork or similar material or where metal inserts are provided to limit compression.

Gaskets are to be as thin as possible consistent with the provision of a good seal, and full details of all gasket sealing arrangements shall be shown on the Plant drawings.

2.3.6. EARTHING TERMINALS

Two earthing terminals, each capable of carrying the full lower voltage fault current for a period of not less than 30 seconds, shall be provide. They shall be located one on either side, and near to the bottom of the transformer to facilitate connection to the local earthing system.

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tank at an approximate height of 1.5 m above ground level:

(a) A rating plate bearing the data specified in IEC 60076-1. This plate shall also

include a space for the Purchaser's serial number

(b) A diagram plate showing in an approved manner, the internal connections

and the voltage vector relationship of the several windings with the transformer voltage ratio for each tap and, in addition, a plan view of the transformer giving the correct physical relationship or the terminals.

(c) A plate showing the location and function of all valves and air release cocks

or plugs. This plate shall also warn operators to refer to the Maintenance Instructions before applying the vacuum treatment specified in clause 2.3.1. above.

2.4. COOLING SYSTEM

2.4.1. GENERAL

All radiators shall be detachable and isolating valves shall be provided to allow removal of radiators with the transformer tank full of oil. The radiators shall be cleaned and treated in accordance with General Technical Requirements for finishing.

Radiators shall be designed so that all painted surfaces can be thoroughly cleaned and easily painted in situ with brush or spray gun. The design is to avoid pockets in which water can collect. Capability of radiator to withstand the pressure test is also required.

2.4.2. RADIATORS/FORCED AIR COOLERS CONNECTED DIRECTLY TO TANK

Radiators connected directly to the tank on transformers shall be detachable. Plugs shall be fitted at the top and at the bottom of each radiator for filling and draining and an isolating valve shall be provided on the tank at each point of connection to the tank to permit removal of radiator.

At the nominal power, dismantling of one of the radiators shall be possible without causing the temperature to rise above permissible values.

2.4.3. AIR BLOWERS

At nominal power, switching off one blower shall be possible without causing temperature to rise above permissible values.

Air blowers for use with oil coolers shall be of approved make and design, be suitable for continuous operation out of doors and shall be capable of dealing with the maximum output and head required in service. They shall also be capable of with-standing the stresses imposed when brought up to speed by the direct application of full line voltage to the motor.

Air blowers shall be complete with all necessary air ducting, and to reduce noise to the practical minimum, motors shall be mounted independently from the coolers or alternatively, an approved form of anti-vibration mounting shall be proved.

It shall be possible to remove the blower complete with motor without disturbing or dismantling the cooler structure frame-work.

Blades shall be of galvanized steel unless otherwise approved. Ducts and Blower casings shall be made of galvanized steel of thickness not less than 2.6 mm and shall be suitable stiffened by angles or tees.

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the blades. Guards shall be designed such that neither blades nor other moving parts can be touched by the test finger illustrated in IEC 60529.

2.4.4. COOLER CONTROL

Where multiple fan cooling using small single-phase motors is employed, the motors in each cooling bank shall preferably be grouped so as to form a balanced three-phase load.

Each motor or group of motors shall be provided with a three-pole electrically operated contactor and with control gear of approved design for starting and stopping manually.

Where forced cooling is used on transformers, provision shall be included under this contract for automatic starting and stopping from the contacts on the winding temperature indicating-device as specified in clause 2.6.1. The control equipment shall be provided with a short time delay device to prevent the starting of more than one fan, or group of fans in case of multiple-fan cooling, at a time.

Where small motors are operated in groups, the group protection with alarm shall be arranged so that it will operate satisfactorily in the event of a fault occurring in a single motor.

The control arrangements are to be designed to prevent starting of motors in total more than 15 kW simultaneously either manually or automatically.

All contacts and other parts need periodic inspection, renewal, or adjustment shall be readily accessible.

All wiring for the control gear accommodated in the marshaling kiosk together with all necessary cable boxes and terminationsand all wiring between the marshalling kiosk and the motors shall form part of the Contract Works.

2.5. VOLTAGE CONTROL

2.5.1. GENERAL

The transformers shall be provided with on-load tap changing equipment for varying the effective ratio while on load, but without producing phase displacement.

The tap changer shall be connected at the neutral side of HV (primary) winding and shall be of the high-speed resistor transition type.

On-load tap selectors shall be contained in separate tanks mounted in the main transformer tank through the top, in an accessible position. The same oil type will be used as for the main tank.

On-load tap changers shall be suitable for specified power flow in both directions. All variables and aspects required for reliable operation at site such as step

voltage, breaking capacity, rated through current, voltage class, etc. shall be fulfilled.

Only design which has been type tested in accordance with IEC 60214 will be accepted.

The tap selector shall be so arranged as to permit easy access for maintenance and repair of the equipment thereon, without the necessity of lowering the oil level in the main transformer tank. Oil in tap selector tanks separate from the main transformer tank shall be under a slight head of pressure from the conservator tank and the design shall ensure that any gas formation or air leaving the tap

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